Cellulose fiber cans



March 1967 J. B. FELTON, JR.. ETAL 3,311,033

CELLULOSE FIBER CANS Original Filed Nov. 12, 1963 FIG. FIG: 2 FIG. 3

JOSEPH B. FELTON, JR. JOHN F. TURNER ARCH/E O. OUNOAN, JR. BY R065 RBART JOHN H. ROBERTS AGENT United States Patent 15 Claims. (Cl. 93-391)This is divisional application of the copending application of Joseph B.Felton, Jr., et al. filed Nov. 12, 1963, Ser. No. 322,705.

This invention relates to methods of preparing containers which can beemployed in the packaging of thermally processed foods.

The familiar tin can has proved to be a very effectual and economicalpackage for a great variety of products. In recent years, however, otherless costly containers have been developed which have replaced the tincan for the packaging of certain of these products. These newlydeveloped containers have been constructed primarily of paper orpaperboard in combination with metal foil or thermoplastic resincoatings, and are now being employed widely for packaging suchdiversified products as motor oil, frozen fruit juices, and'refrigeratedbakery goods. While the tin can has lost some markets to fiber cans, thetin can remains essentially unchallenged in its use for packagingthermally processed foods. The less expensive fiber cans have hithertobeen incapable of withstanding the rigorous conditions involved inthermal processing and the only competition at all with the tin can inthis area of use has been from the more expensive glass containers andaluminum cans.

Thermal processingof foods involves cooking of the food product after ithas been sealed in the can or container, so as to destroy all organismsthat might cause spoilage. The exact conditions employed in thermalprocessing vary considerably depending primarily upon the particulartype of food product being canned. However, regardless of the type offood being canned, thermal processing involves the use of relativelyhigh temperatures in the presence of water or steam, resulting ininternal and external pressures being alternately applied to the can.The temperatures and related conditions employed in thermal processingrequire the use of cans constructed from materials having much betterphysical characteristics than are provided by present fiber based cans.

A fairly typical example of conditions encountered in thermal processingis in the canning of peas. The first step is to blanch the peas at atemperature of about 160 F. Peas at this temperature are then packedinto the can with hot water. While still open, the cans are exhaustedusually by heating in a steam chamber or by passage of a steam jet overthe open end to remove any air. The cans are next sealed and processedin a stream autoclave at 240 F. for varying lengths of time, dependingon can size, to destroy any injurious organisms. ,At the temperatureemployed in this last step a gage pressure of about 8 p.s.ig, isdeveloped in the autoclave. As the liquid in the can is heated, analmost equal pressure is built up within the can. The net result is thatvery little pressure differential exists While the can remains in theautoclave. When the sealed can is removed from the autoclave, however,the pressure on the outside of the can is rapidly decreased toatmospheric while the contents of the can, still being at about 240 F.maintain the internal pressure of about 8 p.s.i.g. As the can cools theinternal pressure in the can decreases, finally becoming zero, andpasses to a negative interior gage pressure, or vacuum, due to thecooling of the contents to a temperature below that at which the canswere sealed.

The can structure must consequently be able to withstand the efiects ofhigh temperature, high humidity and moisture, pressure and vacuum. Thecharacteristics of paper, paperboard, and similar non-woven cellulosefiber webs are such that both high temperature and humidity or waterhave a significantly detrimental effect on the strength propertiesresulting in severe loss of ability to withstand the pressure andvacuum. To our knowledge, no presently available fiber can constructionis consistently capable of performing satisfactorily under theconditions of thermal processing. While it is conceivable that, bygreatly increasing the quantities of materials employed in the availablefiber cans and by encapsulating the cellulose web so as to eliminate allcontact of steam or water with the web, a can could be made which wouldprovide satisfactory service, such cans would be wholly impractical dueto their great bulk or high cost.

The primary object of the present invention is to provide a method forproducing a can constructed of non- Woven cellulose fiber web materialwhich can practically be employed for packaging of thermal processedfoods and Which can compete with the common tin can.

Other objects will become apparent from the following disclosure.

We have found that a can capable of being employed in the packaging ofthermal processed foods and in substantially all other packaging uses inwhich the tin can is currently employed can be constructed from pressurecured thermosetting resin-impregnated non-woven cellulose fiber webs.

In the practice of this invention, non-woven cellulose webs, such aspaper and paperboard, are impregnated with a thermosetting resin and theresin cured under pressure in the web structure. The resultant thinsheets of cured resin-impregnated web can thereafter be cut to size, andformed into the desired shape to make the body wall of a can. Thefinished can is ultimately produced by the attachment of the requiredend or ends which may be made of the same resin-impregnated web materialas that employed in the can body, tinplate, aluminum, or any othersuitable materials such as high temperature-resistant molded plastics.While, in general, the basic steps employed inconverting the thin sheetsof resin-impregnated web into a can body are similar to those employedin making cans from tinplate, the great difierences in the properties ofthe impregnated webs used in this invention compared to those oftinplate require that significantly different methods be employed inconducting these basic steps, asywill be evident from the disclosurehereinbelow.

The non-woven cellulose fiber webs employed in this invention possesscertain characteristics which would apparently make them totallyunsatisfactory for use under the conditions involved in thermal processpackaging. Cellulose fibers derived from any source, whether they arethe naturally occurring pure fiber of cotton or the pulp obtained bystringent chemical treatment of wood,

- are seriously effected by both heat and moisture; the two conditionswhich are characteristic of thermal processing. Non-woven cellulosefiber webs which are produced by the felting of a large number ofsubstantially individual cellulose fibers derive their strength from themechanical entanglement of the fibers with one another and fromphysio-chemical bonding of the fibers to one another at their points ofcontact. Both of these fiber-to-fiber bonding mechanisms are seriouslyaffected by moisture and/ or heat. For example, paper can lose up to 90%of its strength by soaking it in water and may lose about 30% of itsstrength by subjecting it to an environment at 220 F. In addition, thedetrimental effects of both moisture and temperature are greatlyincreased when they occur in conjunction with one another as isencountered during thermal processing.

In spite of these inherent disadvantages in the characteristics ofnon-woven cellulose webs, these webs when combined with thermosettingresins in accordance with the principles of this invention cansatisfactorily be utilized in making cans for thermal process packaging.

A wide variety of thermosetting resins may be employed in the practiceof this invention. Satisfactory resins include the allyl resins whichare based upon such diallyl prepolymers as diallyl phthalate or diallylisophthalate and which are cured to the thermoset state with peroxidecatalysts, the amino resins (excluding urea-aldehyde resins which lackthe required resistance to moisture) which are based upon the reactionof a polyamine such as melamine and an aldehyde such as formaldehyde,the epoxy resins which are based upon the polymerization of prepolymershaving a plurality of oxirane groups, such as the diglycydyl ether ofbisphenol, under the influence 'of cross-linking agents or catalystssuch as acids or amines, the urethane resins which are based upon thepolymerizing reaction of polyisocyanates with compounds having aplurality of active hydrogens such as the polyhydroxy polymers of ethylene or propylene glycol or of polyhydroxy and polybasic acidiccompounds, the polyester resins including the oil modified polyestersgenerally referred to as alkyd resins, which are based upon thecrosslinking of copolymers, formed by the reaction of a polybasic acidand a polyhydric alcohol, through unsaturated groups in the cop'olymergenerally by vinyl compounds, the phenolic resins which are based uponthe reaction of a phenolic compound with an aldehyde such asformaldehyde, those therm'osetting polycarbonate resins (as contrastedto the thermoplastic polycarbonate plastics) which are based upon thereaction between unsaturated and aliphatic dehydroxy compounds withphosgene or appropriate phosgenederived precurors, and the organopolysiloxane based silicone resins.

- 'For practical purposes, the selection of a thermosetting resin foruse in this invention will be based primarily upon economicconsideration of the current cost of the resins and the quantity ofresin needed to impart the necessary properties to the cellulose web.Based upon current costs and knowledge, the preferred resins for use inthis invention are the phenolic resins which are relatively inexpensiveand can be employed at reasonably low levels. These phenolic resins maybe employed at levels as low as 15% while still producing satisfactorycans, depending upon the service intended. (As employed herein thepercentage of resin is the weight percent of the cured resin solidsbased upon the total weight of the cured resin solids and the celluloseweb). Below 15 the moisture resistance is inadequate to withstand therigorous conditions of thermal processing. Levels of up to about 60%phenolic resin may be employed satisfactorily; however, above about the35% level improvement of properties is 4 generally insufficient tojustify the added cost. A level of between 20% land 30% phenolic resinhas been found to be preferred. The other thermosetting resins should beemployed within the same broad range as the phenolic resins, i.e.,between 15% and although the preferred range may be somewhat different.

The resin-impregnated web stock may be constructed of a single ply or aplurality of plies laminated together into a unified coherent sheethaving no sharply defined planes of demarcation throughout its thicknessof either properties or composition. Such a laminated structure does notnecessarily have to be homogeneous, and may have gradual gradations bothin composition and properties through out its thickness. This is truealso of impregnated web stock made from a single ply.

In order to achieve the necessary properties for withstanding theconditions of thermal processing, it is de sirable that the resin bedistributed throughout the cellulose web. The necessity of suchdistribution .of the resin will be quite evident when it is recalledthat both the heat and moisture conditions encountered in thermalprocessing cause severe deterioration of cellulose fiber-to-fiberbonding. Such deterioration of the bond; although it may be in only arelatively small portion of the web could result in functional failureof the whole structure. The fact that the resin must be dispersedthroughout the web does not mean that the resin distribution must beuniform therethrough. It is quite possible to vary the type of resin orto employ reduced amounts of resin in the interior of the web where thefibers are not subjected to the effects of heat and moisture to as greata degree as on the surfaces of the web.

It is essential, in order to obtain web stock capable of withstandingthe thermal processing operation, to cure the thermosetting resin undersufficient pressure to compact the web structure into a substantiallyvoid-free contiguous structure. The pressures necessary to achieve thistype of dense structure, which should have a dry specific gravitygreater than about 1.05, is greatly dependent upon the flow and curecharacteristics of the resin. Pressures as low as 50 p.s.i. are marginalalthough they may be employed with some of the resins at rather highresin percentages. Preferably much higher pressures should be employed,in the neighborhood of 500 1500 p.s.i., especially for phenolic resins.Maximum pressures are limited to those at which compressive degradationof the fibers occurs. The pressures specified need not necessarily beemployed on a constant basis throughout the curing of the resin as it ispossible to reduce the pressure to a much lower level after the initialhigh pressure has caused flow of the resin and has compacted the web.While this second phase lower pressure can be considerably lower thanthe initial pressure, it should be sufficient to prevent any substantialspring-back of the fibers from their compressed state and should becontinuously applied until the curing of the resin has proceeded to thestage wherein the resin bonding is strong enough to restrain thetendency of the fibers to assume their original configuration in thenon-compressed web.

The temperature employed for curing the resin-impreg nated webs will,'of course, be dependent upon the specific type of resin employed. Somefew resins, such as the resorcinol-resins and certain of the epoxy andpolyester resins, can be cured at or near room temperature. However,these resins will present obvious problems in preventing precuring ofthe resin during impregnation of the web and subsequent removal ofsolvent. Most of the thermosetting resins will require curing attemperatures from about to 400 F., as recommendetd by the resinsupplier.

A relatively simple test has been developed to determine the utility ofcured resin-impregnated web materials in cans subject to thermalprocessing. This test consists of cutting 1" x 3" strips of Web Stock,subjecting them to saturated steam at 212 F. for 5 minutes in a closedconer conditioning for 3 days in an atmosphere at 50% relative humidityat 73 F.) and after such steam treatment the modulus of elasticityshould not be less than 500,000 p.s.i. Web stocks which do not retain atleast 65% of their original modulus of elasticity do not possessadequate water resistance properties to perform satisfactorily inthermal processing applications. Likewise, these web stocks which do nothave a minimum modulus of elasticity of 500,000 p.s.i. after theaforementioned steam treatment, lack adequate rigidity to withstand thevacuums encountered in thermal processing applications. It could bepointed out that the 65% retention of the original modulus of elasticityand the minimum 500,000 p.s.i. modulus of elasticity after steamtreatment are minimum requirements for the Web stock; such as for use inthe canning of fruit juices, and that web stocks which barely meet theserequirements will not in general, be satisfactory under more severeconditions of thermal processing such as encountered in the canning ofmeats when a temperature of 260 F. is employed for an extended period oftime, and pressure differential as high as 20 p.s.i.g. are involved. Tooperate satisfactorily under the more severe conditions it would bedesirable for the web stock to retain at least 90% of the modulus whichshould not be less than 1,000,000 p.s.i. after the steam treatment.

Due to the anisotropic nature of the properties of nonwoven cellulosefiber webs and the cured resin-impregnated web stock obtained therefrom,the modulus of elasticity in fiexure as used herein is the average ofmoduli taken at right angles to one another, preferably in the machinedirection and cross machine direction in the case of paper andpaperboard.

While the impregnated web materials of this invention are capable ofwithstanding the effects of steam, water and temperature without loss ofutility, they are not necessarily completely impervious to water,particularly where the resin content is at the lower end of the rangeset forth hereinabove. Water consequently can be transmitted through thecan walls by wicking action of the cellulose fibers. This permeabilityto water is unrelated to the fact that the impregnated web material isat the same time essentially impermeable to atmospheric gases. Thisproblem, of water permeability, however, is readily solved by providinga thin water impermeable coating on the side of the impregnated webmaterial that is to be in contact with the aqueous content of the can.This coating may be composed of any of the wide variety ofwater-impermeable materials available, such as polyvinylidene, epoxy,polyester, oleo, and alkyd resins and metal foil, which would besuitable for use in contact with food. Preferably a thin layer ofaluminum foil is used. This can be easily applied by laminating it tothe impregnated web material during the pressure curing of the resinimpregnated web. By use of this method the foil can be integrallylaminated to the resin impregnated Web without the need for a separateadhesive.

The conversion of the cured resin impregnated web stock into canspresents certain problems which are not encountered in making of cansfrom the presently employed tinplate. Forming these webs into thedesired shapes for can bodies is much more difficult due to the factsthat (1) the impregnated web stock is considerably thicker, on the orderof 1.5 to 3 times as thick as the tinplate and that (2) thestress-strain relationship of the impregnated webs is entirely differentfrom that of tinplate. The modulus of elasticity of tinplate is on theorder of 25,000,000 to 30,000,000 while that of impregnated web stocksuitable for this invention ranges from about 500,000 to 2,500,000. Ascompared to the resinimpregnated web stock of this invention then,tinplate requires a much higher stress to produce a given deflection inthe area of non-deformable flexure. The stress-strain curve of tinplate,moreover, has a broad area from the point at which deformable flexurebegins until rupture occurs. This broad area of deformable flexurepermits fiat tinplate to be easily bent into the can body shape andpermanently deformed into that shape. This region of deformable fiexure,however, is very limited in the stress strain-relationship of theresin-impregnated web stock at room temperature and permanentdeformation of the web stock is much more diflicult to achieve withoutrupturing the stock.

Due to the limited deformability of the impregnated web material at roomtemperature and to the interrelated factor of physical properties towithstand pressure forces, it has been found that the thickness of theimpregnated web material must be controlled in its relation to thediameter of the can being made. The thickness of the can wall should beless than of the can diameter and preferably in the range of to Webthickness greater than of the can diameter will cause problems informing the can shape and in providing an economic package.

Thisinvention may be better understood by referring to the drawingswherein- FIGURES 14 are top cross-sectional views of cans illustratingmethods of forming a side seam.

FIGURES 5-8 are partial front elevations taken in section of methods offastening the can end.

Production of cured resin-impregnated web stock satisfactory for use inthis invention can be prepared by a number of methods well known in theprior art. One method is to employ the current techniques used in thelaminating industry to produce flat sheets of material which can then becut and formed into the can body. Obviously, it would greatly reducecosts to form a convolute or spiral tube from a non-curedresin-impregnated web and cure the resin during the tube formation.However, such methods, except for those wherein the tube is subsequentlycured in a tube press for considerable time under substantial pressure,will not yield products which possess the necessary properties specifiedhereinabove. As currently available tube pressing methods are incapableof the large scale economical production needed for cans, forming of canbodies from flat pressed sheets is the preferred method.

In making the can body from flat, cured, resin-impregnated web stock, itis necessary that the stock be cut into the appropriate size for the canbody, the cut section formed into the cylindrical shape of the can body,and the edges permanently joined together creating a side seam 20.

The methods of forming side seams in tin cans are quite obviously notapplicable to the material of this invention since this material can notbe soldered. Joining the edges together may be simply accomplished,however, by applying an adhesive to the edges, bringing the edges intocontact with one another, and maintaining this contact until theadhesive is set. It will be obvious that the adhesive employed must beable to withstand the heat and moisture conditions of thermal processingwithout failure. Consequently, it is generally preferable to employ anadhesive of the thermosetting type. The melanine and epoxy resins havebeen found to be especially well suited for this use.

Simple butt glueing of the edges together will generally not providesufiicient side seam strength in the can. It is consequently necessaryto employ other methods of glueing. Several satisfactory methods areshown in FIG- URES 1 through 4 of the drawings. In FIGURE 1, a simpleoverlap seam is illustrated when the inner surface of one edge is gluedto the outer surface of the opposite edge of the can body. In FIGURE 2 amodified butt joint is shown which has a reinforcing strip 22 glued overthe butt joint. This particular joint may be further modified by use ofa tear string 24 which can be pulled to separate the reinforcing stripalong the seam line to promaterial.

vide foreasy opening. The seams illustrated in FIG- URES 1 and 2 havethe undesirable characterisic of cansing a protrusion in the area of theseam due to the multiple thickness of material. This protrusion, whichis also characterisic of the common tin can, often causes difficulty inthe opening of cans with the common types of canopeners and createsdifliculties in providing a hermetic seal. This protrusion can easily beeliminated, however, by use of the constructions shown in FIGURES 3 and4 employing a beveled joint and a ship lap joint respectively. As thebeveled joint is more easily prepared, and better controlled, it is thepreferred type for use in this invention.

Once-the. can body 21 has been formed, the completed can ready forfilling, is formed by attaching one or more end closures 25, 25, Theseend closures may be formed of metal, plastic or cured impregnated webstock similar to that employed in the can body. Many differentexpedients may be employed for attaching the end closures; a few ofwhich are illustrated in FIGURES 5 through 8. The presently preferredmethods of attaching the end closure 25 are shown in FIGURES 5 and 6employing a standard can end of tinplate or aluminum. Either of theseclosures can be made on double seaming equipment currently employed inmanufacturing tin cans.

In FIGURE 5 the gasket material employed on the standard can ends ofordinary tin cans is replaced by an adhesive 26 such as a thermosettingepoxy resin. The end is placed on the can body and a so-called falsedouble seam made by folding the edges of the end under adjacent portionswithout disturbing the edge of the can body. While it is not necessaryto make the false seam, this provides several distinct advantages. Thefalse double seam not only maintains the closure in place durterminaledge portion of the can body is flanged prior to attachment of the lidand is mechanically interlocked with the can end during double seamingin the same manner as is commonly used on standard tin cans. Utilizingthis method of attaching the can end, an adhesive need not be employedalthough it is preferable to do so or to employ a gasketing materialsimilar to that employed in metal cans. It will be obvious that the bending of the edge of the can body through 180 at the very small radiusinvolved places a severe strain on the cured resin-impregnated web stockemployed in the can body. In fact, it is very interesting that, due tothe high rigidity and limited deformability of the can body stock ofthis. invention, such an interlocking arrangement can be made withoutultimate failure of the can body along the bend. This is particularlytrue when it is considered that this bending involves compound curvatureof the However, it has been found that some cured resin-impregnatedpaper webs will undergo such compound curvatures without detrimentalresults by properly controlling tthe manufacture of the curedresin-impregnated web stock. Of primary importance in accomplishing theflanging of the can body is the type of resin employed. For satisfactoryflanging without cracking at the fold line, it is necessary to useeither a highly plasticized resin or one having relatively highdistortion characteristics at elevated temperatures above thetemperature to be employed in thermal processing. In the latter caseflanging is easily accomplished at an elevated temperature of-about 300to 350 F. The plasticizers used to develop the necessary bendingcharacterisics may be either exand moisture resistance generally causedby the commonly employed external plasticizers.

A method of internal plasticization which has proved to be extremelyeffective with phenolic resins has been to utilize a phenol having analkyl group attached in the manufacture of the phenolic resin. It isgenerally preferable not to employ such modified phenols as the solesource of phenolic materials due to the increase in cost withoutsubstantial improvement is plasticity after a level of 50% alkylatedphenol has been reached. To achieve significant improvement inplasticity at least 10% of the phenolic material used in making theresin should be of the alkylated type. Suitable alkylated phenols arethose which contain a side chain of from about 4 to 15 carbon atoms.Particularly suitable have been those having side chains in the middleof this range namely octyl or nonylphenol.

An additional factor which influences the ability of the can stock towithstand the deformation during interlocking with the can end isquantity of resin employed. Contrary to expectation, the greater thequantity of resin emjoyed in the cured web stock, the easier it will beto form such an interlock. Consequently, it is preferred practice whenemploying the closure shown in FIGURE 6 that the resin loading beincreased to a level between about 30 to 50%. Other well known methodsof securing the can end 25 to the body such as those in FIGURES 7 and 8may be employed.

The following examples illustrate the methods of manufacturing curedresin-impregnated web stock and the conversion thereof into cans.

Example 1 A 195 lb./ 3000 sq. ft. paper web was impregnated with aphenolic resin varnish and dried to provide a ratio of :28:8 parts byweight of paper phenolic resin, and volatiles, respectively. Thephenolic resin was prepared from phenols, formaldehyde, and sodiumhydroxide at a mole ratio of l.'l.845:0.04.

In preparing this resin a kettle was charged with the following:

Lbs. N-onyl phenol 17.25 Phenol, 92% U.S.P 75.00 Flake paraformaldehyde,91% 49.41 Water 14.25

This mixture was preheated to at which time 2.60 lbs. of 50% sodiumhydroxide was added in six equal portions at 5 minute intervals. Afteran additional 14 minutes of cooking, the kettle temperature was raisedfrom 160 F. to F. in 3 minutes and kept at 180 F. for 22 minutes. Thekettle was then cooled to room temperature. The prepared resin contained5.4% free formaldehyde and 63.4% solids.

The resin was then diluted to 47% solids With methanol, and the pH wasadjusted to 8.3 with the use of concentrated HCl.

The paper web was passed through a trough containing the above resinvarnish. A series of scraper bars and a set of squeeze rolls were usedto provide uniformity of impregnation. The amount of resin pickup wascontrolled by adjusting the web speed and scraper bars. The impregnatedweb was dried to the desired volatile content with the use of twosequential drying cabinets, the tem perature of which was controlled at275 F.

The continuous dried resin-impregnated paper was cut into flat sheets.Two of these sheets faced on one side with a thin sheet of aluminum foilwere pressed together to provide stock for the making of can bodies.

Pressing was accomplished at a temperature of 320 F. for 7.5 minutesemploying a pressure of 1500 =p.s.i.

This laminated web stock was used in the fabrication of cans in thefollowing manner:

The laminated stock was cut into a rectangle of appropriate size for canbody construction. The two opposite sides of the can body blank whichform the side seam of the can were beveled with parallel slopes so thatthe width of the bevel was approximately 12 times the thickness of thelaminate.

An adhesive, which was composed of a melamine formaldehyde resindissolved in water, was applied to both of the beveled edges.

The can body was formed by curling the body blank into a cylinder withthe aluminum foil surface on the inside and aligning the beveled edgesso that when bonded the thickness of the side seam was essentially thesame as that of the body material. The side seam was bonded by elevatingthe temperature to 320 F. while applying a pressure of 150 p.s.i. to theoverlapping beveled area. This combination of heat and pressure effectedcure of the adhesive, permanently bonding the side seam.

A double seamer was used to attach the metal ends to the unfiangedcylinder by a false double seam. The same adhesive used for the sideseam was used to bond the metal end to the can body. This adhesive wasapplied inside the lip of the can end in lace of the conventionally usedgasketing compound.

Size 303 x 406 cans fabricated in the above manner were pressure testedand easily withstood internal pressures up to 70-p.s.i.g. and externalpressures up to 20 p.s.i.g. with no structural failure. Cans were alsoemployed for the thermal processing of diced carrots and performedsatisfactorily with no failures occurring. The conditions employed inthis thermal processing operation consisted of filling and sealing ofthe cans at 180 F. and steam retorting at 240 F. for 20 minutes.

Flexure test run in accordance with ASTM 790-61 on samples of web stockprepared in the above manner, and conditioned in a standard atmosphere,revealed an average modulus of elasticity of 1,960,000 p.s.i. Aftersteam treatment, the average modulus of elasticity was found to be1,340,000 p.s.i.

Example 2 A 195 lb./3000 sq. ft. paper web was impregnated with a resinvarnish to provide a ratio of 10012818 parts paper, resin, andvolatiles, respectively.

A phenolic resin was prepared which was prepared from phenol,formaldehyde and sodium hydroxide at a mole ratio of 1:1.845:0.04. Inpreparing this resin a kettle was charged with the following:

Lbs. Phenol, 92% U.S.P 89.7 Flake paraformaldehyde, 91% 53.4 Water 12.6

This mixture was preheated to 160 F. at which time 2.81 lbs. of 50%sodium hydroxide was added in six equal portions at minute intervals.After an additional 14 minutes of cooking, the temperature of the kettlewas raised to 180 F. in 2 minutes and kept at this temperature for 16minutes. The kettle was then cooled to room temperature. The resultingresin varnish contained 6.7% free formaldehyde and 61.2% solids.

This resin was mixed at a solids weight ratio of 1:1 with a kraft pinelignin. This varnish was then diluted with methanol to a solids contentof 50% and the pH adjusted to 6.0 with the use of concentrated HCl.

The same method as described in Example 1 was used to impregnate thepaper web, press the laminate, and fabricate the can.

Flexure tests conducted on web stock prepared in the above mannerrevealed an average modulus of elasticity after standard conditioning of1,700,000 p.s.i. and after steam treatment, an aver-age modulus ofelasticity of 1,420,000 p.s.i.

Example 3 A 150 lb./ 3000 sq. ft. paper web was impregnated with a resinvarnish to provide a ratio of :40zl0 parts paper, epoxy resin, andvolatiles, respectively. The epoxy resin varnish was prepared bycombining 100 parts of a diglycidyl ether of bisphenol type epoxy resinprepared by reacting bisphenol and epi'chlor-ohydrin having an epoxideequivalent of -192, and 43 parts of a reactive polyamide resin. Thesecomponents were diluted to 30% solids with methyl-ethyl ketone beforetreating. a

Two sheets of the above impregnated paper web and a sheet of aluminumfoil were pressed in the same manner as described in Example 1 with theexception that the press time was extended to 15 minutes instead of 7.5minutes.

Cans were fabricated from this high pressure epoxy laminate in the samemanner as described in Example 1.

Tests conducted on these cans revealed that internal and externalpressures of 50 p.s.i.g. and 12 p.s.i.g., respectively, were withstoodwithout failure. No difficulty was encountered in retorting dicedcarrots in these cans.

Flexure tests conducted on web stock prepared in the above mannerrevealed an average modulus of elasticity after standard conditioning of1,340,000 p.s.i. and, after steam treatment, an average modulus ofelasticity of 1,000,000 p.s.i.

We claim:

1. The method of producing cans suitable for packaging of thermalprocessed foods which comprises impregnating a non-woven cellulose fiberweb with a thermosetting resin, curing under pressure the resin in atleast one such resin impregnated web while in a flat state to produce aunified sheet having from 15 to 60% thermoset resin dispersed throughoutsaid sheet, said sheet having a specific gravity of at least 1.05 andwhich after conditioning in a saturated steam atmosphere at 212 F. forfive minutes will have a modulus of elasticity in fiexure of at least500,000 which is in excess of 65% of the original modulus of elasticityin flexure prior to such conditioning, forming said cured resinimpregnated sheet into a cylindrical shape ad hesively securing oppositeedges of the sheet together to form a cylindrical can body, andattaching a can end to said can body.

2. The method of claim 1 wherein metal foil is laminated to said resinimpregnated web by pressing it with said web during the curing of theresin and the cam body is formed so that the aluminum foil constitutesthe interior surface thereof.

3. The method of claim 1 wherein a water impervious coating is appliedto the interior surface of the can body.

4. The method of claim 1 wherein the cured resin impregnated sheet has amodulus of elasticity after steam conditioning of 'at least 1,000,000p.s.i.

5. The method of claim 1 wherein the thermosetting resin is a phenolicresin.

6. The method of claim 5 wherein the cured resin impregnated sheetcontains from 20 to 30% thermoset resin.

7. The method of claim 5 wherein from 10 to 50% of the phenoliccomponent of said phenolic-resin is an alkylated phenol having from 4 to15 carbon atoms in the side chain.

8. The method of claim 7 wherein the alkylated phenol is octyl phenol.

9. The method of'claim 7 wherein the 'alkylated phenol is nonyl phenol.

10. The method of claim 1 wherein the resin in said resin impregnatedweb is cured at 100400 F. under a pressure of 500l500 p.s.i.

11. The method of claim 1 wherein the opposite edges of the sheet aresecured together in the forming of the can body in a manner that thethickness of the wall of the can body is substantially uniformthroughout the circumference of the can body.

12. The method of claim 1 wherein the diameter of the 1 B. 1 2 canformed is from 100 to 200 times the thickness of the References Cited bythe Examiner f; ifi i a 1 h th t t f UNITED STATES PATENTS eme o 0 cairnW erein e resin con en 0 both surfaces of the cured resin impregnatedsheet is 1,200,803 10/1916 Besozzl 93-94 X greater than the resincontent of the interior of said sheet. 5 i i 14. The method of claim 1wherein the resin content one L 2,367,419 1/1945 Morreii 9339.1

fit salvlheureytli.l resin giplrlegnated sheet is substantially uni-2,393,347 1/1946 Stuart et a1. 93 39Il I W S 9- 2,766,807 10/1956 Marian156184 X 15. The method of claim 1 wherein the resin content of2,801,946 8/1957 Evenblij 93 391 X both surfaces of the cured resinimpregnated sheet is at 10 57 2 5 19 2 Leibl-eich 93 39 1 least equal tothe resin content of the interior of the sheet.

' BERNARD STICKNEY, Primary Examiner.

1. THE METHOD OF PRODUCING CANS SUITABLE FOR PACKAGING OF THERMALPROCESSED FOODS WHICH COMPRISES IMPREGNATING A NON-WOVEN CELLULOSE FIBERWEB WITH A THERMOSETTING RESIN, CURING UNDER PRESSURE THE RESIN IN ATLEAST ONE SUCH RESIN IMPREGNATED WEB WHILE IN A FLAT STATE TO PRODUCE AUNIFIED SHEET HAVING FROM 15 TO 60% THERMOSET RESIN DISPERSED THROUGHOUTSAID SHEET, SAID SHEET HAVING A SPECIFIC GRAVITY OF AT LEAST 1.05 ANDWHICH AFTER CONDITIONING IN A SATURATED STEAM ATMOSPHERE AT 212*F. FORFIVE MINUTES WILL HAVE A MODULUS OF ELASTICITY IN FLEXURE OF AT LEAST500,000 WHICH IS IN EXCESS OF 65% OF THE ORIGINAL MODULUS OF ELASTICITYIN FLEXURE PRIOR TO SUCH CONDITIONING, FORMING SAID CURED RESINIMPREGNATED SHEET INTO A CYLINDRICAL SHAPE ADHESIVELY SECURING OPPOSITEEDGES OF THE SHEET TOGETHER TO FORM A CYLINDRICAL CAN BODY, ANDATTACHING A CAN END TO SAID CAN BODY.